My a3 sport still loosing water

Hi bad news lifted the bonnet this morning to top the pissers up and noticed the the coolant had drop slightly again, I've only had it back 2 weeks from the garage I brought it from, after the 1st time it went in they replaced the egr cooler, came back and still lost water, then went back and the said the head gasket had gone so they took the head off and sent it away to be pressure test properly ad get it overhauled and skimmed, as they were aware of the dreaded head cracks on that model engine, when I picked it up they said it may still use a little water as the system it purging, is that normal, but they never changed the water pump nor the cam belt as they said because its a warranty claim the warranty company won't pay for the cam belt, ****ers, but that's not the point my point is should it of used a little water like they stated, if not what else can it be that's leaking, rads fine, and the matrix is fine, unless its the water pump, or worse still the head is actually cracked and they are covering there own ****, help me cos this is driving me mad as I have always been a audi fan but this is making me want rid,

Oh nealy forgot, should the system be pressurising, because the water level does drop but when te cap is loosened it hisses and the level pops back up to where it should, but this morning it did hiss but the level only went up to the min mark, should it be doing this if not why when its had all that work done, and why is it still leaking

Yeh I have been opening it when cold, at least it's normal for there to be pressure in it, and for it to raise when opened, ill just keep an eye on it,